The successful operation of satellite communication networks, such as time division multiple access (TDMA) systems, depends upon the ability of the receiver equipment at the respective sites to be accurately tuned to the incoming signal from another site. Because a TDMA system employs burst communications it is not possible to use a conventional automatic frequency adjustment mechanism which relies upon the presence of a continuous carrier. Consequently it has been a common (and extremely costly) practice to provide each site with a high precision oscillator which monitors an effectively perfectly stable pilot frequency transmitted from a master site and determines the offset through the satellite.
One proposal to eliminate the need for a precision oscillator at each site and thereby reduce the expense of the equipment at the remote sites is described in the Luginbuhl et al, U.S. Pat. No. 4,509,200, entitled `Satellite Telecommunication System`. Pursuant to the patented scheme a high precision pilot tone oscillator is installed at a central site, the only apparent purpose of which is to measure frequency offset (drift) through the satellite. By monitoring the pilot tone over a loop back to itself the master site is able to measure the offset through the satellite, which must be corrected. The measured error is then transmitted as an information signal for use at the remote site. The remote site must strip off the data and then use the data to properly tune itself (not having the benefit of a precision local oscillator). This presupposes that the remote site is properly tuned to begin with, something that the coarse oscillator used by the remote site cannot guarantee. Consequently, the procedure is questionable, at best.